SI-8578 Avoid fresh name clashes under -Ydelambdafy:method

It is important to append the fresh 'N' after '$'. Otherwise, we
find out the hard way that ("foo$11" + "1") == ("foo$1" + "11").
SI-8578 Avoid another potential fresh name clash

No test case for this one, but see the preceding commit for
the class of bug that I'm trying to avoid.
Merge pull request #3742 from retronym/topic/8578

SI-8578 Avoid fresh name clashes under -Ydelambdafy:method